As illicitly manufactured drugs are marketed and transferred from hand to hand without any manufacturer's identification and specification and as it is not possible to distinguish visually sugar, salt, heroin, crack, and cocaine, it is necessary to examine the presumptive drug substances in a laboratory. The crime laboratories, however, are often very busy so that such drug tests may take too long to keep the suspects meanwhile in custody. Many police agencies have therefore turned to test the presumptive drugs themselves. Thus, chemical spot test kits have been commercially developed which shall allow an easy identification of narcotics and drugs of abuse. Many law enforcement agencies are using these kits as the investigator can now easily check the suspected drug substances within minutes. Conventional test kits for detection and identification of cocaine are commonly based on contacting the suspected substance with a cobalt thiocyanate solution. The formation of a relatively water insoluble turquoise complex indicates the presence of cocaine or its salts. As the cobalt thiocyanate test is relatively simple, it is also in use outside the laboratories. Notwithstanding, there is a great demand for a more specific test kit.
The standard Scott test is based on a colour reaction with cobalt thiocyanate (L. J. SCOTT (1973), Specific Field Test For Cocaine, Microgram, VI, 179). The corresponding commerical test kit contains the necessary chemicals in three prefilled hermetically sealed glass ampules or tubes and comprises the following steps:
Step A. The first tube contains cobalt thiocyanate in a solution of 1:1 water and glycerine which forms a characteristic blue precipitate with salts of cocaine.
When the cobalt thiocyanate is dissolved in water alone, a blue precipitate is formed with nearly every alkaloid substance. The addition of glycerine (1:1) to the aqueous reagent, however, reduces the solubility of most drug substances other than cocaine to almost zero, so that these other substances cannot participate in a falsely positive colour reaction. By this way, it is possible to exclude drugs such as heroin, methadone, quinine etc. However, cocaine stays soluble in such a mixture of water and glycerine and can give a good response.
Crack, which is a cocaine base, reacts with Scott's reagent slower and with less colour intensity. The addition of acid, however, converts crack to its salt and enhances its colour reaction.
L. J. Scott reports that four drugs in this stage will react with the same colour reaction as cocaine: (1) phencyclidine (PCP); (2) dibucaine; (3) butacaine; (4) methapyrilene. The two steps below shall exclude these four drugs:
Step B. By adding concentrated hydrochloric acid, the initially blue solution is converted into a clear pink solution.
Step C. By adding chloroform the blue complexed cocaine is partitioned into the organic phase.
The Scott test has several disadvantages. L. J. Scott himself reports that (i) the ratio of solution A to B is critical. When an excessive amount of hydrochloric acid (solution B) is added to solution A, after the colour reaction with cocaine, a blue rather than a pink solution is formed, and the blue will no longer be extractable into the chloroform layer after the addition of solution C. (ii) On the other hand, when an excessive amount of cocaine is present in step A, it can be sometimes necessary to add two additional drops of hydrochloric acid which makes the test prone to errors. (iii) Furthermore, Scott has only tested a limited number of drugs. Since then, it has been found that also some other compounds can give a blue colour with Scott's reagent, e.g. dixyrazine.
With the cobalt thiocyanate reagent of ODV Inc., which is hereafter called "Scott's modified reagent", procaine, tetracaine and methadone give a colour reaction similar to cocaine. Thus, this single reagent cannot really serve as a specific colour reagent for the identification of cocaine, since false positive results are also obtained with substances that have similar response characteristics.
The European Patent No. 0 233 063 discloses a process and kit for the presumptive identification of cocaine or heroine street drugs. This process comprises applying to the sample to be tested a reagent, comprising a sulfonated aromatic pH indicator which gives a characteristic colour reaction in the presence of trace amounts of organic bases or acetic acid. The process provides a quick test for the detection of street drugs which can then, for example, be followed by the Scott's test. In order to deal with the increasing number of similar street drugs, i.e. in their base form, it has become necessary to combine several tests to exclude false positive results.
The deficiencies of these tests have led the inventor to develop another specific reagent, which is intended to be used in combination with Scott's reagent or Scott's modified reagent, in order to screen out false positive results in the Scott reaction. This other specific reagent allows surprisingly an error-free positive identification of cocaine and its salts.